In semiconductor processing systems, particularly those operating under high vacuum conditions, semiconductor wafers must be transferred into and out of process modules where steps in the manufacturing process take place. Since the cost of wafer processing is dependent on the throughput of the system, it is imperative that wafers be removed from each process module as soon as each module has completed processing the wafer which was loaded into it. Such transfers to/from processing modules are performed by so-called transfer robots.
Conventional transfer robots were typically designed to transfer only one wafer at a time, or to transfer two wafers at a time but only simultaneously (i.e., not asynchronously). Typically a number of process modules are mounted around the perimeter of a transfer chamber containing a transfer robot. Hence, for enhanced system throughput, it is common to configure the transfer robot to be capable of transferring wafers into process modules at fixed relative orientations to each other (e.g., side-by-side, or at 180° separation around the transfer chamber perimeter).
FIG. 39 is adapted from U.S. Pat. No. 5,993,141, and shows a conventional dual wafer robot 3910, which is limited to wafer handling within a single plane. In the following description, let x represent either a or b in FIG. 39. Linear track, section 3912x is pivotally mounted to a rotatable stage 3914 by pivot pin 3916x. Motorized platen 3918x is slidably mounted on linear track section 3912x and carries an end effector 3920x on a leading (outer) edge. The upper surface of linear track section 3912x includes a linear bearing 3922x, along each of the longitudinal edges thereof to guide the motorized platen 3918x. The central portion of track section 3912x includes a plurality of raised metal edges 3924 (preferably formed of a ferromagnetic material), disposed in a spaced, parallel relation to one another and substantially perpendicular to the linear bearings 3922x. A plurality of coils (not shown) in motorized platen 3918x electromagnetically interact with raised edges 3924 to drive platen 3918x along the track section 3912x. The extension and retraction motions of end effectors 3920a and 3920b of this robot may function asynchronously, but are limited to operation with both end effectors 3920a and 3920b being in the same plane since both linear track sections 3912a and 3912b are attached to rotatable stage 3914.
FIG. 40 is adapted from U.S. Pat. No. 6,071,055, and show's a portion of a dual wafer robot 4010 that is limited to wafer handling in a tandem configuration with simultaneous motion of both wafers in the same plane. The dual wafer robot 4010 is housed in transfer chamber 4012, shown with three dual wafer process chambers 4014 attached. Transfer of wafers into/out of process modules 4014 is through vacuum valves 4016. Note that this dual wafer robot design, with both end effectors locked together in a U-shaped assembly, inherently must transfer both wafers: (1) simultaneously, (2) in the same plane, and (3) only into a single dual-wafer process module 4014.
FIG. 41 is adapted from U.S. Pat. No. 5,678,980 and illustrates a dual wafer robot that is limited to single wafer loading and unloading. In this design, end effector 4110 is supported and moved by outer arms 4114 and 4116. Similarly, end effector 4112 is supported and moved by outer arms 4118 and 4120. Outer arms 4114, 4116, 4118 and 4120 are attached to, and moved by, center arms 4122 and 4124.
In view (A) of FIG. 41, center arm 4124 is rotating (arrow at upper center) counter-clockwise around pivot 4126, while center arm 4122 is rotating (arrow at lower center) at the same speed clockwise around pivot 4126. The combined motion of arms 4122 and 4124 causes outer arms 4114 and 4116 to extend end effector 4110 as shown by the left arrow. Simultaneously, outer arms 4118 and 4120 are retracting end effector 4112 as shown by the right arrow. Because the outer arms 4114, 4116, 4118, and 4120 are longer than central arms 4122 and 4124, end effector 4110 moves much farther outwards than end effector 4112 moves inwards.
In view (B) of FIG. 41, center arms 4122 and 4124 are rotating (arrows at center) in the opposite directions from view (A), thus end effector 4112 is extending (right arrow), while end effector 4110 is retracting (left arrow) towards the center.
In view (C) of FIG. 41, center arms 4122 and 4124 are positioned 180° relative to each other, making the radial positions of end effectors 4110 and 4112 the same. Arms 4122 and 4124 are rotating clockwise (arrows at center) at the same speed, causing end effectors 4110 and 4112 to rotate clockwise around pivot 4126 (arrows at left and right).
Note that in this dual wafer design, the wafers are restricted to a 180° orientation, and only one end effector can be extended at a time (while the other end effector must be retracted). Also, for pick-and-place operation (where a processed wafer is removed and another wafer is immediately placed into a process module), it is necessary to rotate the robot a full 180° to insert a wafer following removal of a processed wafer, thereby decreasing system throughput.
FIG. 42 is adapted from U.S. Pat. No. 5,794,487 and illustrates a dual wafer robot 4210 that is limited to single wafer loading and unloading (i.e., one which cannot load two wafers simultaneously). Lower arm link 4212 is connected to base 4214 through shoulder 4216, which enables 360° rotation. Upper arm link 4218 is connected to lower arm link 4212 through elbow 4220, which enables relative motion between upper arm link 4218 and lower arm link 4212. Two end effectors 4222 are mounted with a 180° relative orientation on central support 4224, which contains wrist 4226. Extension and retraction of end effectors 4222 is effected by changing the angle between upper arm link 4218 and lower arm link 4212. Thus, in this dual wafer robot, only a single wafer can be loaded or unloaded at a time, since if one of the two end effectors 4222 is extended, the other end effector 4222 is necessarily retracted at the same time.
FIG. 43 is adapted from U.S. Pat. No. 5,539,266 and illustrates a robot actuator having two motors, each requiring a magnetic air-to-vacuum coupler separate from the robot motors. In particular, this actuator includes two coaxial magnetic couplers for driving the robot mechanism. The coupler mechanism consists of two primary rings 4312 and 4314 of permanent magnets located outside the vacuum chamber wall 4316 (i.e., in air) and mounted for rotation about a common axis 4318.
For example, first primary ring 4312 may be mounted on a flanged shaft 4320, driven by motor M2 4322. Second primary ring 4314 may be mounted on a flanged bushing 4324 that is driven by motor M1 4326, where flanged bushing 4324 is rotatably mounted on shaft 4320. Motors M1 4326 and M2 4322 are servo motors of conventional design.
Both primary rings 4312 and 4314 include a large number of permanent magnets oriented radially with alternating N and S poles directed outwards. Flux rings 4328 and 4330 provide flux return paths for the permanent magnets in primary rings 4312 and 4314, respectively. All components 4312, 4314, 4320, 4322, 4324, 4326, 4328 and 4330, are mounted outside of vacuum wall 4316 (in air).
Secondary ring 4332 includes flux return path 4334 and a plurality of permanent magnets (the same number as in primary ring 4312). Secondary ring 4336 includes flux return path 4338 and a plurality of permanent magnets (the same number as in primary ring 4314). The permanent magnets in secondary rings 4332 and 4336 are attracted through vacuum wall 4316 to the permanent magnets in primary rings 4312 and 4314, respectively. Angular movements of primary rings 4312 and 4314 are thereby coupled to secondary rings 4332 and 4336, respectively. Angular movements of secondary rings 4332 and 4336 are coupled to the in-vacuum robot actuation mechanism.
Note that in this prior art robot drive mechanism, the drive motors are completely separate from the function of coupling motion through vacuum wall 4316. For each of the two magnetic couplers, two sets of permanent magnets are required: one set directly coupled to the motor (but not part of the motor), and a second set directly coupled to the robot actuator and magnetically coupled to the first set of permanent magnets.